The Tunability of Surface Plasmon Polaritons in Graphene Waveguide Structures

The tunability of propagation properties of surface plasmon polariton (SPP) modes in a waveguide formed by two parallel graphene layers separated by a dielectric layer is studied. For this purpose, the dispersion equation of the structure is numerically solved and the effects of applied bias voltage, the role of effective structural parameters, and electron–phonon scattering rate on the propagation of symmetric and antisymmetric SPP waves are investigated. The results of calculations show that considering the electron–phonon scattering rate as a function of Fermi energy and temperature leads to a considerable decrease in the propagation length of SPPs. As the main result of this work, tuning the propagation characteristics of SPPs is possible by varying any of the parameters such as applied voltage, thickness of insulating layer between two graphene layers and permittivities of dielectric layers, and finally the temperature. It is found that antisymmetric mode benefits from a larger propagation length in comparison with that of the symmetric mode.

     

Ultra-Uniform Field Distribution in a Finite-Width Metal–Dielectric–Metal Waveguide

We investigate the propagation characteristics of the fundamental surface plasmon polariton (SPP) mode of a finite-width metal–dielectric–metal waveguide. By changing the refractive index or the thickness of the dielectric layer of the waveguide, the SPP mode can be transformed from a mode confined in the dielectric layer into a mode confined around the metal corners. There always exists a condition at which the mode field distribution in the dielectric layer becomes almost perfectly uniform along the direction parallel to the metal layers, and this condition is insensitive to the width of the waveguide. It is also possible to obtain an ultra-uniform field distribution by controlling the refractive index of a different dielectric placed on both sides of the waveguide. The waveguide can be used as a basic structure for the realization of nanosized photonic devices and sensors.     

A Surface Plasmon Microcavity Between the Toroidal and Flat Metallic Surfaces

We consider the formation of the surface plasmon polariton (SPP) mode in the structure with a metallic torus and a metallic flat surface separated by a dielectric medium. The energy of the wave field is mainly concentrated in the dielectric medium at the vicinity of the minimum thickness of the gap between the metallic surfaces. The dependence of the resonant frequency on parameters of the structure was determined. The strongly localized SPP mode in the transverse direction contributes to the increase in the Purcell factor that is crucial for enhancement of the spontaneous emission rate.     

Two-Dimensional Analogies to Frequency-Selective Surfaces (FSS) on the Graphene Sheet

In this paper, we propose that two-dimensional analogies to frequency-selective surfaces (FSS) can be achieved on graphene surfaces based on transformation optics. The analogies to representative FSS structures, including the anti-reflecting coating (ARC) and the high-reflecting coating (Bragg reflector), have been investigated through both analytical effective-index method (EIM)/transfer-matrix method (TMM) and numerical simulations. Both analytical and numerical solutions have shown that the propagation of plasmons on graphene surface with periodic chemical potentials can be an analogy to the interaction of incident light with traditional FSS multilayer dielectric media in which the transmission or reflection can be obtained by EIM/TMM. Combined with the tunability of graphene, the transmission or reflection of plasmons can be tuned by adjusting the bias voltage. The proposed structures and theoretical methods may provide new visions for achieving two-dimensional analogies to traditional structures on graphene.

     

基于纳米多孔硅Bragg反射镜免标记生物传感器的研究

构建一种基于多孔硅Bragg反光镜的免标记的纳米生物传感器,通过在纳米多孔硅上固定的适配子的特异性识别能力,检测溶液中四环素浓度。当适配子结合不同浓度的四环素溶液时,引起多孔硅Bragg反光镜内部有效折射率的变化,反射谱峰位进而发生变化。传感器的有效检测范围为1~200μg/L,检测限为1μg/L。     

Surface Plasmon Polariton Modes at Interface of a Metal and an Ambichiral Sculptured Thin Film

The excitation of surface plasmon polariton (SPP) at interface of a metal and an ambichiral sculptured thin film was theoretically investigated in the Kretschmann configuration using the transfer matrix method. The dependence of SPP modes for a P polarization plane wave on the incident angle of light and the angle of rise of nanocolumns of ambichiral dielectric medium was reported. We found that multiple SPP modes are excited at the interface of metal and ambichiral dielectric medium. The results of phase speed as a function of pitch showed only that a SPP mode can be excited at all pitches.     

Near-Field Coupling Method for Subwavelength Surface Plasmon Polariton Waveguides

A near-field coupling method for studying propagation properties of surface plasmon polariton (SPP) in subwavelength dielectric-loaded SPP waveguides (DLSPPWs) is presented. In this method, a tapered fiber probe is employed to generate a nanometer optical spot. When this spot is near the entrance of the DLSPPW with its polarization parallel to the waveguide, a strong guiding wave is observed by a leakage radiation microscope. For DLSPPWs with a dielectric height of about 600 nm, we observed SPP waves with zigzag propagation patterns at 650 nm wavelength. Such zigzag propagation results in a great reduction of propagation loss. In addition, the zigzag wave has a strong optical confinement. The bending loss for an L-bend DLSPPW is only about 0.4 dB.     

Hybrid Plasmonic Waveguide Based on Tapered Dielectric Nanoribbon: Excitation and Focusing

The nanofocusing of light source was proposed and simulated using the dielectric-loaded surface plasmon polariton (SPP) model with various laterally tapered planar dielectric architectures on the top surface of the metal. By using finite-difference time-domain method, enhancement factor for the local electric field under distinctive incident polarization was analyzed with different taper apexes under various incident wavelengths and incident angles of the excitation laser. The SPP dispersion and the effect of dissipation on adiabatic nanofocusing of SPP in a sharp taper structure were used to predict the optimal taper angles of the structure and to explain the phenomena of SPP wave slowing down as it propagating toward the taper end. This SPP nanofocusing process was also experimentally realized by illuminating the structure of a tapered CdS nanoribbon deposited on the Ag surface. As the emission of the focused SPP at the taper end, the proposed plasmonic structure can be severed as a light nanosource emitter in the future optical integrated circuits.     

Surface Plasmon Polariton Waveguide by Bottom and Top of Graphene

Semiconductor surface plasmon polariton (SPP) waveguide has unique optical properties and compatibility with existing integrated circuit manufacturing technology; thus, SPP devices of semiconductor materials have wide application potential. In this study, a new integrated graphene SPP waveguide is designed using the bottom and top roles of graphene. Moreover, a T waveguide structure is designed by InGaAs of semiconductor gain, with rectangular GaAs material on both sides. The structure adopts light to stimulate the SPP, where its local area is enhanced by the interaction between two interface layers and a semiconductor gain and where its frequency can be adjusted by the thickness of the graphene. Characteristic analysis reveals the coupling between the T semiconductor gain and the SPP mode. The propagation distance of the waveguide can reach 75 cm, the effective mode field is approximately 0.0951λ ², the minimum of gain threshold is approximately 2992.7 cm^?1, and the quality factor (FOM) can reach 180. The waveguide structure which provides stronger localization can be compatible with several optical and electronic nanoscale components. That means, it can provide light for surface plasmon circuit and also can provide a great development in the low-threshold nanolaser.     

多孔硅Bragg反射镜适配子生物传感器检测心肌肌钙蛋白I

通过脉冲腐蚀法制备多孔硅Bragg反射镜,将心肌肌钙蛋白I（cTnI）适配子共价固定到多孔硅Bragg反射镜的孔洞中,发现适配子能与cTnI分子特异性结合。定量分析不同浓度的cTnI与适配子结合后多孔硅Bragg反射镜的反射谱峰位的红移情况。结果表明：基于多孔硅Bragg反射镜适配子生物传感器的光学检测具有良好的特异性,且具有免标记及检测时间短等优异性能。传感器的线性检测范围0．05-4nmol／L,最低检测限为0．05nmol／L。     

Design of a Slit-Groove Coupler for Unidirectional Excitation of the Guided Surface Plasmon Polaritons Through a Plasmonic Slot Waveguide

In this paper, a plasmonic-photonic nanostructure has been introduced for efficient unidirectional coupling of free-space radiation to surface plasmon polariton (SPP) waves under normal illumination on a subwavelength slit. The structure consists of a conventional metallic slit-groove nanostructure integrated with a plasmonic waveguide to support SPP waves along the desired direction with a remarkable lateral confinement. The unidirectional coupling is achieved by using an integrated plasmonic distributed reflector designed under Bragg condition. This reflector basically distributes part of the light coupled through the slit into the SPP modes of the waveguide. Numerical simulations show that up to 26 % of the normally incident light couples to the transversely localized field of the surface plasmon. In addition, the ratio of mode current density of the surface plasmon, launched in the desired direction, to that in the opposite direction can reach about 23 times. This structure shows a 2.5-fold improvement in coupling efficiency relative to a standard slit-groove structure. Also, the transmission distance for the new nanostructure is shown to be more than 8 times greater than that of the standard nanostructure.     

Attenuation of Bragg backscattering of electromagnetic waves from density fluctuations near the region of polarization degeneracy in magnetoactive plasma

Specific features of Bragg backscattering under conditions of strong polarization degeneracy near the cutoff surface in an anisotropic medium are studied analytically and numerically. It is shown that the linear interaction of normal waves can substantially affect wave scattering by suppressing the amplification of Bragg backscattering near the cutoff region in the case of weak coupling between normal waves.     

Conditions for Loss Compensation of Surface Plasmon Polaritons Propagation on a Metal/Gain Medium Boundary

One way to compensate for the surface plasmon polariton (SPP) propagation losses is to use a gain medium. However, simply ensuring high enough gain is not sufficient because it may violate the bounded character of the wave. Therefore, a detailed theoretical analysis is needed for the determination of the conditions for lossless or amplified SPP propagation. Here presented is an exact theoretical analysis of the SPP propagation in the case of an infinite metal/gain medium boundary. It is shown that the conditions for lossless/amplified SPP propagation can be conveniently examined and presented as a simply connected region in the complex plane of the gain medium dielectric function. Effective and minimum gain parameters are introduced, which facilitates the simultaneous analyses of different gain media/metals combinations. The practical application of these results is illustrated for several gain media/metal (silver, gold and aluminium) systems.     

Surface Plasmon Effects Excited by the Dielectric Hole in a Silver-Shell Nanospherical Pair

Using the finite-element method, the surface plasmon effects in a three-dimensional silver-shell nanospherical pair with five different dielectric holes (DHs) that interact with a transverse magnetic mode incident plane wave are investigated. The proposed structure exhibits a red-shifted localized surface plasmon that can be tuned over an extended wavelength range by varying the dielectric constant and the radii in DHs. The increase in the near-field intensity is attributed to a larger effective size of DH that is filled with a higher refractive index medium. The predictive character of these calculations allows one to tailor the shape of the nanoparticle to achieve excitation spectra on demand with a controlled field enhancement.     

An Ultra-Wideband Terahertz Metamaterial Absorber Utilizing Sinusoidal-Patterned Dielectric Loaded Graphene

In this paper, a non-structured graphene sheet loaded with a sinusoidal-patterned dielectric is introduced as an ultra-wideband metamaterial absorber in terahertz regime. Regardless of conventional structures with multilayered-graphene, a single layer sheet of non-structured graphene is used whereas the proposed structure benefits from dielectric width modulation and cavity method in order to excite continuous graphene plasmon resonances. The structure comprises four layers that two Fabry-Perot cavity mirrors are constructed by upper sinusoidal-patterned dielectric and a gold film. Full wave simulation results demonstrate that a broadband over 90% absorption with absolute bandwidth of 6.58 THz and central frequency of 3.97 THz is achieved under normal TE/TM incident plane wave. The designed structure yields 166% relative bandwidth. According to the symmetric configuration, the absorption spectra of mentioned polarizations are thoroughly close to each other resulting to a polarization insensitive structure. The stability of bandwidth and absorbance of the structure versus angle of incidence, θ, up to 35°/65° for TM/TE polarizations, respectively, and azimuth angle, φ, shows an interesting capability for utilization as detectors and sensors. The simple geometry of utilized graphene layer results in easy fabrication. The designed structure has wideband absorption in THz regime. Moreover, it is more compact than conventional broadband THz absorbers.

     

Surface Plasmon Polariton Mach–Zehnder Interferometer and Oscillation Fringes

We present a quantitative experimental analysis of a surface plasmon polariton (SPP) interferometer relying on elliptical Bragg mirrors. By using a leakage radiation microscope, we observe oscillation fringes with unit visibility at the two interferometer exits. We study the properties of the SPP beam splitter and determine experimentally both the norm and phase of the SPP reflection and transmission coefficients.     

Three-Dimensional Manipulations of Surface Plasmon Polariton Wave Propagation

The plasmonic integrated circuit, a potential application of surface plasmon polaritons (SPPs), can manipulate an SPP wave propagating on a metal surface in a way similar to electronic circuits. Here, we propose the concept of three-dimensional (3D) SPP wave manipulation: control of an SPP wave propagating in both the horizontal direction and the vertical direction. A hole set in the film can guide an SPP wave in the vertical direction. In the horizontal direction, two holographic groove patterns are used to focus an incident SPP wave on one surface of the film to the hole and control the divergent SPP waves transmitted from the hole on the other metal surface, respectively. The holographic groove patterns are designed via the methodology of surface electromagnetic wave holography. 3D finite-difference time-domain method simulations show a good performance of the 3D manipulation via these designed holographic groove patterns.

     

Surface Plasmon Polariton Propagation at the Interface of a Metal and an Ambichiral Nanostructured Medium

The propagation of a surface plasmon polariton wave at the interface of a metal and an ambichiral nanostructured medium was theoretically investigated in the Kretschmann configuration using transfer matrix method. The dependence of optical absorption linear polarization on structural parameters was reported. The results were compared with those obtained from the interface of a metal and a chiral dielectric medium as a reference structure. We found that multiple plasmon modes are excited at the interface of metal and ambichiral dielectric medium. Our calculations revealed that there exist five plasmon modes for chiral, trigonal, and tetragonal structures; three plasmon modes for pentagonal structure; two plasmon modes for hexagonal structure; and one plasmon mode for dodecagonal structure that propagate with different phase speeds. The obtained results showed that only one plasmon mode occurs at all pitches, while other modes exist at some of the pitches of anisotropic chiral and ambichiral dielectric mediums. The time-averaged Poynting vector versus the thickness of metal film confirmed that the energy of photons of incident light is transferred to surface plasmon polariton quasiparticles and the surface plasmon polariton wave is localized at the interface of metal and ambichiral dielectric medium.     

Surface Plasmon Polariton Emission Prompted by Organic Nanofibers on Thin Gold Films

The excitation of surface plasmon polaritons (SPP) at a gold?Cvacuum interface by femtosecond light pulses mediated by organic nanofiber-induced dielectric perturbations is observed using interferometric time-resolved photoemission electron microscopy. The experimental data are quantitatively reproduced by analytic simulations, where the nanofibers are considered as superior source of the SPP emission. The flexibility and tuneability of phenylene-based nanofibers in their morphology and intrinsic optical properties open up future applications to fabricate custom-designed nanoscale sources of SPP.     

Effects of Dielectric Anisotropy on Surface Plasmon Polaritons in Three-Layer Plasmonic Nanostructures

The effects of highly anisotropic dielectric on surface plasmon polaritons (SPPs) are investigated in several three-layer plasmonic nanostructures. Dispersion relations of SPPs in anisotropic-dielectric-metal (ADM), dielectric-anisotropic-metal (DAM), and metal-anisotropic-metal (MAM) structures are analytically derived. The numerical results in the visible indicate that, in ADM, the propagation length of a conductor-gap-dielectric mode is changed from 5.9 to 91 μm and its cutoff thickness from 83 to 7 nm with varying the optical axis, while in DAM, the influences of anisotropic dielectric are reversed on propagation length and cutoff thickness. In MAM, by tuning the optical axis, the light confinement of symmetry SPPs mode varies about 10 %. Further numerical calculations show that the above results induced by the anisotropy of dielectric can be extended to the telecommunication frequency. The improved mode properties may be used in plasmonic-based nanodevices and tunable single surface plasmon sources.